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arXiv 0912.2852astro-ph.IM
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大气色散和相位校准的含义

Atmospheric dispersion and the implications for phase calibration

Emily I. Curtis, Bojan Nikolic, John S. Richer, Juan R. Pardo

摘要:

任何ALMA相位校准策略的成功,其中包括相位转移,取决于对大气路径延迟如何随频率变化的良好理解(例如,Holdaway & Pardo 2001)。我们探讨如何在现实的大气条件下,在ALMA网站使用ATM传输代码的湿色散路径延迟的变化。我们发现湿色散路径延迟成为高频ALMA频段(>160 GHz,频段5至10)的非色散延迟的一个重要部分(> 5%)。此外,除了频带9和10之外,ALMA的4 GHz连续带宽上的色散路径延迟的变化并不显著。对于典型的水蒸气量、水蒸气标度高度和Chajnantor上方的地面压力,色散路径延迟与水蒸气总柱的比率没有显著变化。然而,温度分布,特别是地面温度更重要。考虑到ALMA的辅助校准设备可能存在的限制,在最坏的情况下,色散路径缩放的不确定性将在2%左右,并且在最高频率下对湿路径波动的总体贡献约为1%。

英文摘要:

The success of any ALMA phase-calibration strategy, which incorporates phase transfer, depends on a good understanding of how the atmospheric path delay changes with frequency (e.g. Holdaway & Pardo 2001). We explore how the wet dispersive path delay varies for realistic atmospheric conditions at the ALMA site using the ATM transmission code. We find the wet dispersive path delay becomes a significant fraction (>5 per cent) of the non-dispersive delay for the high-frequency ALMA bands (>160 GHz, Bands 5 to 10). Additionally, the variation in dispersive path delay across ALMA's 4-GHz contiguous bandwidth is not significant except in Bands 9 and 10. The ratio of dispersive path delay to total column of water vapour does not vary significantly for typical amounts of water vapour, water vapour scale heights and ground pressures above Chajnantor. However, the temperature profile and particularly the ground-level temperature are more important. Given the likely constraints from ALMA's ancillary calibration devices, the uncertainty on the dispersive-path scaling will be around 2 per cent in the worst case and should contribute about 1 per cent overall to the wet path fluctuations at the highest frequencies.

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